In a comment at www.drroyspencer.com/2011/09/a-primer-on-our-claim-that-clouds-cause-tem… … Richard Courtney outlines some research on climate models he did ten years ago and some follow-up papers by others, since then. He says none of the models (the IPCC tracks 20 of them) could match mean global average temperatures in teh 20th century if they did not make use of an assumption, namely that cooling is caused by aerosols in the atmosphere. Hence, all the models input a cooling effect on past temperatures – which they might describe as a mysterious impact from clouds. The models differ by the degree of cooling effect they add to the brew – the disguised 'fiddle factor' that allows them to line up the models with temperature records from the past. Courtney thinks the assumption per aerosol is incorrect ( see Energy and Environment, volume 10:5). In 2007 Keihl found something similar (Geophysical Research Letters, volume 34).
Meanwhile, Piers Corbyn has weighed in to the cloud debate by arguing that it isn't cosmic rays but the Sun that is responsible – the solar wind.